The present invention relates to a control method for fuel injection engines of the type used in vehicles such as automobiles and more particularly to a fuel injection control method so designed that the film mass deposited on the wall of the intake manifold is estimated and the desired fuel injection quantity is determined on the basis of the estimated film mass.
The fuel injected from the fuel injection valve is partly deposited on the intake manifold wall or the fuel deposited as the film mass is vaporized and fed into each cylinder thus failing to wholly supply the injected fuel into the cylinder and in particular the quantity of fuel supplied to the engine deviates considerably from the fuel quantity required from moment to moment during the engine acceleration or deceleration.
Conventional techniques heretofore proposed for solving this problem include methods in which the quantity of deposited fuel is estimated and the desired fuel injection quantity is determined on the basis of the estimated deposited fuel (e.g., a fuel injection quantity control method for fuel injection engines disclosed in Japanese Patent Publication No. 58-8238 by Toyota Jidosha Co., Ltd.). In this method, a basic width of the fuel injection pulse supplied to the injector is determined in accordance with the manifold pressure and the engine speed and the quantity of film mass in the intake manifold is estimated on the assumption that the fuel is injected for the duration of the pulse width. However, the actual quantity of fuel injected into the intake manifold is the quantity of fuel injected during the time that the injection valve or injector is opened for the duration of an actual fuel injection pulse width calculated in accordance with the fuel quantity carried over to the engine cylinder, the deposited fuel quantity, a feedback correction factor, etc., as well as the basic fuel injection pulse width. As a result, it is impossible to correctly estimate the actual quantity of film mass unless the method of estimating the quantity of film mass deposited in the intake manifold is such that the actually injected fuel quantity is fed back and a part of the injected fuel quantity is deposited on the intake manifold wall. For these reasons, the conventional estimating method cannot accurately estimate the quantity of film mass and therefore there is a disadvantage that the quantity of fuel supplied to the engine deviates from the required fuel quantity at the moment despite the fact that the fuel injection quantity also takes the quantity of film mass into consideration.
Also included among the conventional fuel injection quantity control methods of controlling the fuel injection quantity by estimating the quantity of film mass are methods in which the desired fuel injection quantity is determined by subtracting the quantity delivered to the cylinder or the carry-over quantity from the quantity of film mass and adding the deposited quantity on the manifold wall to the basic fuel injection quantity (e.g., Japanese Patent Publication No. 58-8238). In this case, of the quantity of fuel injected the quantity of fuel deposition on the manifold wall is of such a nature that it can be accurately determined only after the actual fuel injection quantity has been determined. While this conventional method determines the deposition quantity of fuel supposed to be deposited on the manifold wall on the basis of a basic fuel injection pulse width, there is a disadvantage that the fuel deposited on the intake manifold wall does not represent a part of the actually injected fuel quantity and therefore it is impossible to accurately determine the quantity of film mass (the quantity of fuel deposition).